Phenol-aldehyde, dicyandiamide binder composition



United States Patent 3,223,668 PHENOL-ALDEHYDE, DICYANDIAMIDE BINDER COMPOSITION Joseph P. Stalego, Newark, Ohio, assignor to Owens- Corning Fiberglas Corporation, a corporation of Delaware No Drawing. Filed Apr. 23, 1962, Ser. No. 189,319 Claims. (Cl. 26029.3)

This invention relates to a binder composition, and, more particularly to a hardenable binder composition containing a phenolic resin and monomeric dicyandiamide which composition is especially adapted for use with glass or other vitreous fibers.

Wool-like and board-like masses of intermeshed glass and other vitreous fibers have been manufactured ex tensively heretofore. In their production, fibers of glass or other vitreous materials are made by drawing or flowing streams of a fused, vitreous material through comparatively small diameter orifices, and accelerating the streams exiting from the orifices to cause attenuation thereof to a desired average fiber diameter. The resulting fibers then are associated with a hardenable binder composition, usually a phenol-formaldehyde partial condensation product, and projected onto a foraminous conveyor where intermeshed fibers and associated binder are collected and subsequently heated to convert the binder composition to a hardened, infusible condition. The final heating step can be carried out while the intermeshed fibers and associated binder are compressed to a desired extent, in which case a board-like product having an apparent density as high as about 12 pounds per cubic foot can be produced. If no pressure is applied during the heating step, a wool-like product having an apparent density as low as about one pound per cubic foot can be produced. Various materials of this type have been produced, and have found wide-spread commercial use as both thermal and acoustical insulating materials. The board-like products can also serve a decorative function.

Since the major portion of products of this sort is inorganic and vitreous in nature it might be assumed that such products would have excellent fire resistance. It has been found, however, that such is not the situation. The customary organic binder in these products undergoes a phenomenon which has been described as punking when subjected to elevated temperatures or direct forming ether linkages, and in this matter increases resistflame. Odors and fumes given off on thermal decomposition of the binder are offensive, and are capable of di-scoloring and staining. For example, malfunctions of clothes dryers and heaters have caused overheating of their fibrous glass insulations and decomposition of the binder, with generation of offensive fumes and staining and discoloring of fabrics. These characteristics of such products have deterred and limited their use in many applications where they would otherwise be ideally suited.

A phenolic resin, usually of the phenol formaldehyde type, has been the customary organic resin constituent in binders for use with glass and other vitreous fibers in such wool-like and board-like products. This phenolic resin serves to hold and lock the fibers in strands, intermeshed structures, mats, packs, boards, and the like.

'The term punking is used herein, and in the art, to refer to comparatively rapid oxidation of the binder, with generation of heat, but without flame.

3,223,668 Patented Dec. 14, 1965 Generally, a satisfactory binder composition, in addition to the organic resin constituent, contains other constitucuts for purposes well known in the art, as for instance to control a particular property or properties of a finished product. Such other constituents include fillers, coupling agents, lubricant-s, plasticizers, dyes, and the like.

The present invention is based upon the discovery that dicyandiamide is a highly useful and beneficial constituent for hardenable, phenolic resin binder compositions. A binder composition containing dicyandiamide is not subject to dilutability problems common with prior art binder compositions. In a hardened, cured state, the binder composition exhibits little or no odor and imparts substantially improved durability and punk resistance to Wooland board-like products. Apparently, upon curing or hardening of the binder composition, the dicyandiamide functions as a cross-linking agent for the hardenable phenolic resin by reacting with methylol groups without forming ether linkages, and in this matter increases resistance to thermal decomposition. During curing, the dicyandiamide may also react with any free formaldehyde present, and in this manner significantly lower the odor level of the final products. A relatively large proportion of dicyandiamide can be introduced into the binder composition by comparison with the proportion which can be introduced in the form of a dicyandiamide-formaldehyde condensation product. In addition, all steps necessary to prepare a suitable combined form of dicyandiamide for introduction into the binder composition are avoided. The discovery provides a process of great versatility and flexibility in that binder compositions containing various ratios of dicyandiamide to phenolic resin are readily obtained by simply varying the amount of monomeric dicyandiamide introduced.

It is, therefore, an object of the invention to provide an improved phenolic binder composition.

It is another object of the invention to provide a method for producing an improved phenolic binder composition.

It is a further object of the invention to provide an improved hardenable phenolic binder composition for use with glass or other vitreous fibers, and which includes dicyandiamide.

It is a further object of the invention to provide a method for producing a mass of intermeshed glass or other vitreous fibers bonded and locked together at points of contact by an improved, cured, and hardened phenolic binder composition, which in an uncured state contained dicyandiamide.

Other objects and advantages will be apparent from the description which follows, which is intended only to illustrate and disclose the invention, and in no way to constitute a limitation thereon.

According to the invention an improved heat-hardenable phenolic resin binder composition is provided. Such a composition has a solids content from about 1% 2 to about 50%, and preferably a solids content from about 3% to 30%, and is an aqueous dispersion consisting essentially of a hardenable phenolic resin and from about 10 to 120 parts of dicyandiamide for each parts of the phenolic resin on a dry solids basis. The exact proportion of dicyandiamide to be employed is determined by the particular properties desired in the product and endapplication in which the binder is used. In general, the larger the amount of dicyandiamide in the composition, the better the punk resistance, the lower the odor of the cured product, and also the less offensive its heat-decomposition products. With binder compositions in which the amount of dicyandiamide about equals or exceeds the amount of phenolic resin, generally it is desirable to use the composition shortly after its preparation, as, otherwise, heating is required to avoid a noticeable separation of the dicyandiamide from the composition. Preferably, the binder composition contains from about 15 to about 85 parts of dicyandiamide for each 100 parts of the heat-hardenable phenolic resin.

The. hardenable phenolic resin is one selected from the group consisting of phenol-formaldehyde partial cndensation products and phenol-amino compound-formaldehyde condensation products, and is of a phenolic resole type. Such phenolic resoles are known to the art. In general, a phenolic resole is produced in the presence of a basic catalyst by reaction in an aqueous system of more than one mol of formaldehyde per mol of phenol. A detailed discussion of resoles can be found in The Chemistry of Phenolic Resins, Robert W. Martin, John Wiley & Sons, Inc., New York, New York, 1956 (see in particular pages 8899, and cited references). In general, phenol-amino compound-formaldehyde condensation products are produced by an aqueous alkaline condensation of phenol and formaldehyde to produce a mixture consisting essentially of phenol alcohols. After adjustment of this phenol alcohol mixture to a pH such as to minimize further condensation of the phenol and formaldehyde, melamine or another amino-resin-former is added and the resulting reaction mixture heated to condense the melamine or other like amino compound with the phenol alcohols and any unreacted formaldehyde. The condensation conditions must be sufficient to effect an appreciable condensation of the melamine or other like amino compound, yet the phenol-amino compoundformaldehyde condensation products, so produced, should be of. a state of condensation that they exhibit a high water tolerance. Where punking resistance is a highly important. property, a comparatively high water tolerance is desirable, as preferably one employs a relatively dilute binder composition in. order to avoid using an excessive amount of the binder. The identity of the particular reactants and catalysts employed to produce the heathardenable phenolic resin appears to be of only incidental importance. In most instances, and preferably so, formaldehyde and phenol (hydroxy benzene). are used, although any aldehydes and-phenols producing a hardenable phenolic resole-type partial condensation product are suitable. Such aldehydes for replacement of the formaldehyde in whole or part include: paraformaldehyde, furfural, acetaldehyde, metaldehyde, tetraldehyde, and the like. Such. phenols for replacement of the hydroxy benzene in whole or part include: various cresols, xylenols, resorcinol, and the like. While melamine is frequently used as the amino-resin-former reactant, urea, thiourea, dicyandiamide, and other like amino compounds capable of condensation with phenol alcohols and formaldehyde also can be used in place. of part or all of the melamine. Any of the conventionally employed basic catalysts, for example anyalkali metal hydroxide, such as barium hydroxide, sodium hydroxide, etc. or alkali metal carbonates, or ammonium hydroxide, or like basic condensation catalyst may be used.

The following examples are presented solely for the purpose of illustrating and disclosing the invention.

EXAMPLE 1 A binder composition was prepared in a mixing tank provided with a propeller-type agitator, which tank was first charged with 500 gallons of water and 327 pounds of, dicyandiamide crystals. The water, dicyandiamide and other ingredients, subsequently charged, were stirred constantly during the formulation of the composition.

The water and dicyandiamide were heated to about F. and the following constituents were then added, in the amounts and order listed: 5 gallons of 20 percent ammonium hydroxide, 0.8 pound of gamma-aminopropyltriethoxysilane, 102 gallons of Phenolic Resin A 21 gallons of a 50 percent water emulsion of mineral oil emulsified with stearic acid and ammonium carbonate, and sufficient water, about 300 gallons, to provide a formulation containing about 10 percent solids. Agitation was continued for a few minutes, after the final water addition, to assure substantial uniformity of the completed binder composition. The ratio of monomeric dicyandiamide to Phenolic Resin A was 39:61.

The binder composition produced as just described, was sprayed into a forming hood through which glass fibers were being projected onto a foraminous conveyor. The fibers were collected in the form of a randomly intermeshed wool-like mass associated with the binder composition. The relative proportion of associated binder composition was such that the binder, after cure thereof, constituted slightly in excess of 8 percent of the total wool-like mass. Cure was accomplished in an oven maintained at a temperature of about 450 F. in which the glass fiber and associated binder were exposed for about 5 minutes by passage therethrough and within which the mass was compressed sufiiciently that a boardlike product having an apparent density of about 11 /2 pounds per cubic foot, on the average, was produced. The board-like product passed a standard Fire Underwriter Laboratory Test for a fire resistant ceiling tile, while a similar board-like product produced in an identical way, only from a like binder composition from which the monomeric dicyandiamide was omitted, failed to pass this test.

Similar binder compositions were prepared in substantially the manner described in Example 1, in which the solids content and the ratio of dicyandiamide to Phenolic Resin A were varied over wide ranges. Data fora number of these binder compositions are set forth in the following Tablel:

No difiiculty was encountered in the preparation of these binder compositions whether the aqueous dicyandiamide solution was mixed with the Phenolic Resin A or the Phenolic Resin A mixed with the dicyandiamide solution. It also was noted that nopreparation diflicultywas encountered using solutions of dicyandiamide dissolved in water containing dicyandiamide contents rangingfrom 15 to as high as 65 percent. Thin films of each of these binder compositions were cured on glass slides at cure.

Phenolic Resin A was a phenolrformaldehyde partial condensation product produced from (180 parts of formalin (a 37 percent water solution of formaldehyde), 100 parts of phenol, and 4 parts of sodium hydroxide. The startingv materials were mixed in a suitable vessel, allowedv to stand at room temperature (about 70" F.) for approximately '16 hours and heated at a progressively increasing temperature which. was sufficient to maintain general boiling thereof. Heating was discontinued when the temperature of the reaction mixture reached approximately 180 F. Sodium hydroxide in the reaction mixture was then neutralized with phosphoric acid; the. resulting. neutralizedphenolic resole was filtered; and the water content was adjusted to provide an aqueous solution of '50 percent solids.

5. temperatures between 425 to 500 F., with cure times from 1 to 8 minutes. Each of the hardened cured films of these binder compositions was examined by an expert and found to be of such a nature that it would provide 6 EXAMPLE 2 A binder of the following composition was prepared in substantially the manner described in Example 1:

Water gallons 955 an acce table re inder n eous fibers p cu d b for glass 3 d other vm 5 Dicyandiamide pounds 80 28 ercent amm niu Small samples of unbonded glass fiber mat were dipped G P f gallons in binder compositions 1A, 1B, 1C, 1D and 1E, and ammaiammofigopytnet Oxyslane Ammonium drained. Some of the samples were then cured at 500 Ph R rd E 1 75 F. for 1 /2 minutes and others at 500 F. for 3 /2 minutes. i esm ercent sol S 40 Each sample, after curing of the binder, was placed on T binder compPsltlon had s?hds content of a hot Plate at a temperature of 5500 F with a tubular percent and the ratio of dicyandiamide to Phenolic Resin chimney encircling each of the samples. Odors at the 3- chimney tops originating from the samples were comer F i f was employed to P d pared and evaluated after 10 and minutes. The odors 15 thermal msulamlg f and board iubstafltlany observed were relatively inoffensive and ranged from g: manner descnbed Example Fme W001 glass sweet to a mild stinging odor. In no instance was the ers ,Were f These fibers We're P y odor observed as offensive or as strong and stinging as tnuatlon of Primary filaments by means of a honlontally that from a similar mat made from a like binder from dlrected bl9wmg burner The fibers wem i i which dicyandiamide was omitted. zontally with a spray of the binder composition; fibers Small samples of unbonded glass fiber mat were also and binder ware deposlted and Collected a mpvmg dipped in binder compositions 1F 16, 1H and 1], foraminous conveyor. Cure of the binder in this dedrained and cured at F for 31/2 minutes when posited mass was in an oven at about 425 F. for about examined at ambient conditions, the resulting bonded 4 f i i' f h 1 inat samples appeared to be substantially free from odor. proper 16s 0 me t t lcknes? Corresponding bonded mat samples produced with the mg Oar .produced thls bmder composltlon a same binders, except that the dicyandiamide was omitted reporteil .fonowmg i COKHPaIaQVe had, at ambient conditions, a faint but detectable odor, propemes o a simllar commerclany avallable msuiatmg indicative of free formaldehyde. A comparison of the board also are Included h commerclqliy avallatile flow, stroke cure, and cone efficiency properties of binder 1.30am 2 a: g q ig from a bmder composltlon Contam' compositions 1F through 1] with those of like binder mg no 1 yan laml T M HI compositions from which the dicyandiamide was limited a 6 showed, within about i5 percent, substantially equivalent properties for all of these compositions. Property gfg g k g giif Additional binder compositions were prepared in sub- Example3 Insulating stantially the manner set forth in Example 1, in which Board the ratio of dicyandiamide to Phenolic Resin A was varied over wide ranges. A Shell Mold Test was used to ifii gfig (2) 25 (a) 27 evaluate the strength properties of these binders compo- Compressive Strength As Prepared: sitions. Table II, which follows, tabulates data on these 583 467 compositions and results of these tests, and, for com- Thiclrtess recgrery upon release of 99 0a percen parison purposes, includes data of a representative, simi After 1 Hour Exposure in Steam Aum lar, binder composition from which the dicyandiaimde clfierd t t 7 B. p. 0 com {G55 0 was omitted. thickness .2.-. .1. 500 377 4; Thickness recovery upon release of 10a 99 95 1 The Shell Mold Test" involved diluting the binder com- Y(D- 3.01 2 g1 position to 40 percent solids, and then mixing grams IEHJQIOHLOSNP 24.3 15,3 thereof with 582 grams of small soda lime glass beads to pro- Pfll'tmg Strength /g d a hell molding composition. Portions of this shell mold- AS Prepared 34 81 ing composition were then placed in a heated dog-bone Afterlhoulexposllrelllsteamfiumshaped" shell pattern, and the pattern containing the dog- S ave bone-shaped molding composition was placed in a heated oven fig for cure of the composition. After cure, and separation from 015 Sorptlon (percent) 0 0 the pattern, the shell moldings were tested for tensile stre%%tll1, gi g fi g'gg f g g g ggg g' i fig gfi gff O1 1 This commercially available insulating board difiered from the board vary to some extent possibly as much as 20 percent it a of Examplebichiefly in that it was produced usingabinder composition been found that such Strength measurements are reasonably p $111013 clntazlneddaddgionized phengl-formaldehydc-melamine condensa. accurate and do provide a good and satisfactory basis for coma 1.? i an I 1 notpontam lcyandlamlde' o parison and evaluation of various resins and binder composlopqn mgater mmutes onahot plate at 500 F'lno Smoldermg' tions as to their usefulness with fibrous lass to prepare Punking after5mlnutes onahot plate at 50 0 F.;no smoldering. bonded mat and the like g 4 After exposure to percent relative humidity for 96 hours at 120 F Table II Ratio 01 Cure Conditions Strength Dicyandi- No. amide to Phenolic Tempera- Time Wet Dry Strength ResinA ture F.) (minutes) Break Break Retention (p.s.i.) 1 (p.s.1.) 2

20:80 425 7 3 796 3 908 88 30:70 425 7 864 876 99 35:65 425 7 720 856 84 35:65 425 s 720 s32 87 40:60 425 s 732 788 93 40:60 500 7 576 720 80 45:65 8 388 520 75 50:50 500 7 624 704 88 Comparison 0:100 425 7 688 744 92 l Conditioned at a temperature of 122 F. and a relative humidity of for 16 hours.

2 As molded. 3 Average oi at least two tests.

7 EXAMPLE 3 A binder composition was prepared as follows: a mixing tank, provided with a propeller-type agitator, was charged with 300- gallons of water. The water was formed glass wool produced in the same manner on the same equipment except that its binder composition contained a hardenable melamine-phenol-formaldehyde resin. Table. IV, which follows, sets forth the data.

. 1 e I warmed and 315 pounds of dlcyandiamide crystals were added thereto and dissolved therein. After cooling of Table IV the resulting solution to ambient temperature, about 70 F., the following ingredients, in the amounts and order as listed, were added and mixed therewith, with From binder constant agitation: 1.37 pounds of gamma-aminopropylpq t From binder containing triethoxysilane, 15.3 pounds of ammonium sulfate, 8 property Composition melamipp gallons of 28 percent ammonium hydroxide, 292 gallons 0fEXamp1e3 forgll sl ggt gde of Phenolic Resin B and 400 gallons of Water. This resin completed binder composition amounted to approximately 1000 gallons and had a solids content of about Den jt c f Ignition Loss, percen 6.7 8.4. 16 percent. The ratio of dlcyandiamide to phenolic Thicknessimhes L0 097' Resin B was 2 :77- Fiber Index 51. 32 11.12 131- ameter Preformed glass wool thermal insulation was pro Punking 500,F p1us hot probe: duced with the above binder composition in a conven- At 2" thickness No punking Complete tional manner on commercial production equipment and punklllg.

Wei htloss ercent 0.7 tests were made of the thermal insulation. Like tests, for g p comparative purposes, were made on a commercial pre- Excellent binder compositions and results have also 1 h If m h d been achieved using dicyandiamide and other heat-hard- Phenolic Resin B was a me amine-p enoorma e y e partial condensation product produced from 58 parts of enable phenohc resms IFS/Lead of Phe nohc Resms A aI 1d henol, 123.4c parts or)formgli i (a 3g p%lCbel1t solu tio n (gf B. For example, substituted melamlnes can be used in ol-maldehyde in wa er an 1 par s o arium y 111 e (Ba( OH)2.8H2O). The starting materials were mixed in a lace of l least a of the lamme as reactant suitable vessel a e hetai iifd vllihile cgnsttantlyhs tirsdtbyajaoprigin producing a useful binder constituent of the nature of peller-type a ita or. e e arge rs was eac 0 and maintailled at this temperature for approximately 3 P.he.n0hc Resm also dlcyandlanilde urea borate gua lg then heated g and 25 l for 311% t g nidine, and urea have been used in place of at least a t en heated to and old at" or our-s. t is ime the reaction mixture had a refractive index of 1.4620 and an part the and the resultmg hardellable infra-red absorption analysis thereof indicated that it was P CHOlIC resins have been found to be suitable binder substantially free of unreaeted phenol and also of methylene on tituents, The proportion of dicyandiamide mixed groups. The reaction mixture had a free formaldehyde conh h h h i of approximately g i i gb F reactiontmigtue i l? wit suc eatardenable resins has been varied over t en cooled to approxima e y and hen ra ze wi sulfuric acid to a pH of about 7.5. A 23. 2 part charge of Wlde ranges and h resl'lltmg bmder composltlons and meltilllillile then hwats idded' arid the treisiuli-ng mixtugiei, 1511118 bonded mats and insulation produced therefrom have agi a e was: ea e to an main a he at appro ma e y 1140" ll. for an additional 2 hour period. The reaction prodcan to be exceu.ent' In general the proceduries ucts welilefthetllll coolelg to appgoximateilly is F., and neutra21- set forth in the preceding examples were followed In ized wit ur er en uric aci to a p 0 approximately '7. The reaction products had a free formaldehyde content of Producmg such bmder composltlons and bonded prod iei-pgroxiguatelyc 1%, tpercent. Bialgstfiagtially) all of ti}? imriurg llctsy roxi e ca ays was precip a e as arium en a e, an i the final product was substantially free of soluble ions. This l Wh1ch.j.f0noWS sets forth addltlonal examples final product was then diluted with water to 40 percent solids. of mder composltlons- Table V Example No 4 5 6 7 8 Binder Composition:

100 gal. Dlcyandlamide, 100% solids 22 lb 1 Ammonium hydroxide (28 percent) 4 al Gamma-aminipropyltriethoxysilane 0151b Ammonium sulfate, 100% solids Vinsol, 40% solids Phenolic Resin A, solids 7 1 gaL Phenolic Resin C, 50% solids! Mineral oil emulsion, 50% solids 2 gal, Dye, solids 2 61b Water a) Total solids, percent 6 Ratio of dieyandiamide to phenolic resin .39161 11:89 43:57. Type of bonded product produced App1iance lnfAppliance m- Heavy density Appliance insulatlon. sulatlon. l sulation. insulation. sulation.

1 Vinsol is the residue left after rosin and turpentine distillation of the extract from the heartwood of southern pine stumps which have been left after a lumbering operation and several years seasoning. This residue 15 a hard, friable, high melting (above F.) natural thermoplastic resin. Its chemical composition is a complex mixture of chemically uncharacterized resinous components which include phenols, phenol ethers, and polyphenols.

The approximate composition is as follows:

6% High melting furiural condensate 4% Neutral oils (hydrocarbons, esters and ethers carrying the vinsol odor) 4 Phenolic Resin 0 was similar to Phenolic Resin B, except that dicyandiamide was substituted for the melamine.

It will be apparent that various changes and modifications can be made from the specific details set forth herein without departing from the spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A hardenable phenol-aldehyde resin binder composition, which is an aqueous dispersion containing from about 1 to about 50 percent of solids consisting essentially of a heat-hardenable phenol-aldehyde resin having no more than about 3.6 percent by weight of free aldehyde, and from about to 120 parts by weight of unreacted dicyandiamide for each 100 parts of the hardenable phenol-aldehyde resin, on a dry solids basis.

2. A heat-hardenable, aqueous binder composition for glass and other vitreous fibers, which composition contains from about 3 to 30 percent by weight of solids consisting essentially of unreacted dicyandiamide and a phenolaldehyde resole in a ratio of from to 85 parts by weight of unreacted dicyandiamide to each 100 parts of the phenol-aldehyde resole, said resole having no more than about 3.6 percent by weight of free aldehyde.

3. A method of preparation of a hardenable aqueous binder composition for glass and other vitreous fibers, which method comprises: dissolving from about 10 to 120 parts of monomeric dicyandiamide in water at a sufficiently elevated temperature to dissolve said unreacted dicyandiamide, and mixing the resulting solution with other constituents making up the composition, the other constituents including 100 parts by weight of at least one heat-hardenable phenol-aldehyde resin from the group consisting of phenol-formaldehyde partial condensation products and phenol-amino compound-formaldehyde condensation products, which condensation products have less than about 3.6 percent by weight of free aldehyde.

4. A method for producing a mat of bonded, intermeshed vitreous fibers, which includes the steps of: introducing a heat-hardenable phenol-aldehyde resin binder composition into a fluid mass of vitreous fibers which are being projected towards a collecting surface, the heathardenable phenol-aldehyde resin binder composition being an aqueous dispersion of from about 1 percent to about percent solids consisting essentially of heat-hardenable partial phenol-formaldehyde condensation products having no more than about 3.6 percent by weight of free formaldehyde and from about 10 to 120 parts of unreacted dicyandiamide for each parts of the heathardenable phenol-formaldehyde condensation products on a dry solids basis; depositing the projected fibers in association with the heat-hardenable phenol-aldehyde resin binder composition in a wool-like mass; and heating the mass of fibers and the binder composition associated therewith to convert the latter to a hardened, cured composition.

5. A mass consisting essentially of intermeshed glass fibers having associated therewith the heat-hardenable, aqueous binder composition of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,690,393 9/1954 McGarvey 117-126 3,004,941 10/1961 Mestdagh et a1. 260-293 LEON J. BERCOVITZ, Primary Examiner.

DONALD E. CZAJA, Examiner. 

1. A HARDENABLE PHENOL-ALDEHYDE RESIN BINDER COMPOSITION, WHICH IS AN AQUEOUS DISPERSION CONTAINING FROM ABOUT 1 TO ABOUT 50 PERCENT OF SOLIDS CONSISTING ESSENTIALLY OF A HEAT-HARDENABLE PHENOL-ALDEHYDE RESIN HAVING NO MORE THAN ABOUT 3.6 PERCENT BY WEIGHT OF FREE ALDEHYDE, AND FROM ABOUT 10 TO 120 PARTS BY WEIGHT OF UNREACTED DICYANDIAMIDE FOR EACH 100 PARTS OF THE HARDENABLE PHENOL-ALDEHYDE RESIN, ON A DRY SOLIDS BASIS. 